This invention in one aspect is directed to a process involving microfiltration of skim milk, providing one product which is useful in cheese making and another product which is useful as a source of whey protein. This invention in another aspect is directed to preparing cheese from microfiltration retentate.
In a conventional cheese making process, dilute whey byproduct obtained after coagulation may be subjected to ultrafiltration to concentrate whey proteins (also known and referred to as serum proteins) to produce whey protein concentrate or whey protein isolate. This produces highly variable whey protein products in terms of composition and functionality, leading food manufacturers to use other protein sources.
It is known that microfiltration of skim milk produces a permeate containing significant amounts of native-state whey protein but the only use suggested for the retentate has been the supplementation of normal milk to slightly higher protein levels. This combination of uses does not provide economic viability.
It was a goal of the research leading to the invention herein to provide an economically viable process for cheese making from skim milk which also provides a consistent composition which is sterile and contains a large percentage of the whey protein from the skim milk in highly functional (non-denatured) state. This goal has been accomplished herein by subjecting skim milk to microfiltration to provide a retentate of higher concentration factor than has been described in prior art coupled with in-process acidification to reduce calcium content in the retentate to provide a ratio of calcium to total protein in the retentate which is desired for a cheese product whereby the retentate is useful for cheese making and a permeate is produced which is a good source of native-state whey protein and which has a composition that is not dependent on the kind of cheese being made.
In one aspect, the invention herein is directed at a process for obtaining from skim milk a concentrated milk product useful in cheese making and another product which is a source of whey protein, said process comprising subjecting skim milk to microfiltration and pH reduction during the microfiltration to provide a retentate which is the concentrated milk product and a permeate which is the product that is the source of whey protein. Typically, the microfiltration and pH reduction are carried out to provide a retentate which is concentrated to a concentration factor of 7xc3x97 to 12xc3x97 compared to the skim milk being processed and is depleted in whey protein and contains higher weight percentage of casein compared to the skim milk being processed and to provide a permeate which contains 40 to 80% of the whey protein of the skim milk being processed and typically no or little casein. The pH reduction is effected by adding acidulant and/or starter culture to the skim milk/retentate during microfiltration and is carried out to cause an increased amount of calcium to be in the permeate, and thus reduce the amount of calcium in the retentate and thus provide a ratio of calcium to total protein in the retentate which is desired for the variety of cheese to be made from the retentate. Preferably, the microfiltration is carried out using a membrane of 0.1 xcexcm to 0.2 xcexcm pore size and pH reduction is effected in a manner which minimizes membrane fouling. Very preferably, the microfiltration is carried out to provide a retentate which is concentrated to a concentration factor of 7xc3x97 to 9xc3x97 as compared to the skim milk being processed and pH is reduced to 6.0 by addition of glucono delta lactone and/or starter culture.
In another aspect, the invention herein is directed to a process for making Mozzarella cheese, e.g., low-moisture, part skim Mozzarella cheese, comprising the steps of (a) preparing an admixture of retentate as described above and milkfat to obtain a protein: fat ratio within 15% of that in the final cheese; (b) forming a homogeneous cheesemilk from the admixture; (c) adding acidulant and/or starter culture to achieve suitable and typical acidity in the final cheese being made, of which the pH of Mozzarella including LMPS Mozzarella ranges from 5.0 to 5.7; (d) adding rennet to cause formation of a coagulum; (e) cubing the coagulum and heating and draining whey if drainable whey is present to produce cheese curd of 44 to 56% moisture content; and (f) forming the cheese curd into the final cheese.
As used herein, the term xe2x80x9cmicrofiltrationxe2x80x9d is used to mean a class of filtration that typically uses membrane pore sizes ranging from 0.05 to 0.2 xcexcm and pressures on the upstream side of the membrane ranging from 69 to 690 kPa.
As used herein, the term xe2x80x9cretentatexe2x80x9d is used to mean in relation to a microfiltration process that liquid product of skim milk microfiltration that is the concentrated skim milk feed and which contains all the components typically found in skim milk but with an increased solids mass percentage (as compared to the original skim milk) of casein, whey protein, fat, and minerals (ash), primarily being calcium, phosphorus, and magnesium.
As used herein, the term xe2x80x9cpermeatexe2x80x9d is used to mean in relation to a microfiltration process that liquid product of skim milk microfiltration which contains only those skim milk components that are able to pass through the microfiltration membrane. Permeate from microfiltration of skim milk is typically composed of water, lactose, whey proteins, and minerals (ash), primarily being calcium, phosphorus, magnesium, sodium and potassium
As used herein, the term xe2x80x9cconcentration factorxe2x80x9d is used to mean a reduction in volume from the original volume of skim milk to a volume of (1 divided by the concentration factor) times the original volume.
The xe2x80x9ctotal proteinxe2x80x9d referred to herein can be determined by multiplying total nitrogen determined by macro-Kjeldahl as described in AOACI Official Methods of Analysis, 16th edition (1995) by a factor of 6.38.
As used herein, the term xe2x80x9cacidulantxe2x80x9d means any preformed acid or acidogen in liquid or solid form, that when added to skim milk, retentate, or retentate-based cheesemilk will produce H3O+ ions in the solution, thus causing a decrease in the pH of the skim milk, retentate or retentate-based cheesemilk.